Fig. 2: Fabrication and characterization of the magnetometers.

a Scanning electron microscope (SEM) image of the FeGaB film. b Atomic force microscope (AFM) of a 500 nm × 500 nm region of the FeGaB film. RMS roughness of the FeGaB film is ~540 pm. c In-plain magnetic hysteresis loops measured using a vibrating sample magnetometer (VSM). The lines and scatters correspond to the loops measured along the easy-axis (x) and hard-axis (y) directions respectively. d Schematic of the fabrication process of the magnetometers. e, f SEM and optical microscope images of the fabricated magnetometer, respectively. The slight warping of the SiO₂ microdisk outer edge is due to the stress within the FeGaB film. g Optical transmission spectrum of the fabricated magnetometer, showing an intrinsic Q factor of around 3.37 × 10⁶ for the WGM of the microdisk, in the 1550 nm band under the critical-coupled condition